Compressor discharge temperature monitor and alarm

ABSTRACT

A compressor protection method and system capable of continuously establishing compressor discharge temperature set points based on actual in-service conditions and detecting damaged compressor valves for a given cylinder at each stage of compression. The method and system utilize sensors configured to monitor process property parameters (e.g. temperature and pressure) at the inlet section and outlet section of a compressor stage. The sensors generate monitored signals corresponding to the process property parameters. The method and system utilize a controller configured to receive and process these monitored signals. The controller executes a control logic that uses the monitored signals to either estimate or calculate compressor valve pressure losses for determining internal cylinder pressures, which are used to calculate compressor discharge temperature set points. The control logic compares the monitored temperature to the temperature set points and may generate a warning or normal operation signals based on results of the comparison.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/482,952 filed on May 5, 2011, which is hereby incorporated byreference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

Not applicable.

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to subject matter for pumping fluids, inparticular reciprocating compressors having a separate sensor that isresponsive to the occurrence of a condition or a change in condition ofeither the compressor or the gas being compressed.

2. Description of Related Art

Reciprocating compressors are often utilized to increase the pressure ofa gas by displacing a positive volume of gas by alternatively fillingand discharging a cylinder by the movement of a piston, plunger ordiaphragm. Reciprocating compressors may be either single-stage ormulti-stage, and the cylinders may either be fitted with single ordouble acting pistons.

Within an individual stage, there may be one or more compressorcylinders. In the case of a stage with multiple cylinders, the cylindersmay be arranged in parallel. The cylinders may be lubricated ornon-lubricated and have an inlet (suction) valve and an outlet(discharge) valve. Failure of these valves can have significantconsequences, including the loss of rod force reversals during eachstroke. The loss of rod force reversals will prevent adequatelubrication to the load bearing components, which include the crankshaftmain bearing, the connecting rod bearing, and the compressor crossheadpin. The loss of adequate lubrication at these components will oftenresult in extensive compressor damage and/or failure (e.g. prematurebearing wear or failure, and so forth) leading to forced outages, lossof production, safety risks to workers, inefficient operation,unnecessary maintenance work and high repair costs. Therefore, it is ofcritical importance to detect valve failure and prevent any potentialdamage.

One direct indicator of valve damage or failure is increased compressordischarge temperature. As a result, several protection systems have beendeveloped to detect compressor valve failure by monitoring compressordischarge temperature. One such system utilizes an operator determinedfixed temperature set point that automatically activates an alarm orshuts down the compressor upon detecting a discharge temperature thatexceeds the set point.

However, systems with a fixed operator determined constant temperatureset point are often inadequate to address the reality of actualin-service conditions. In particular, compressor discharge temperaturegenerally does not remain constant over time. Rather, it is typicallyvariable and dependent upon other conditions including gas composition,suction pressure and temperature, and discharge pressure. For example,if a fixed compressor discharge temperature set point has beenestablished based on a suction temperature of 70° F. and the suctiontemperature decreases (or increases) due the to a change in localconditions (e.g. ambient temperature, suction pressure, and so forth),then the set point may be too high (or too low). In the case of a fixedset point that is too low, this may result in a false alarm leading tocostly and unnecessary shutdowns and lost production time.Alternatively, in the case of a set point that is too high, this mayresult in compressor valve failure or damage going unnoticed. Thus, aprotection system with a fixed operator determined temperature set pointdischarge temperature that does not continuously update based onchanging service conditions may be inadequate to protect a compressor.

Another type of compressor protection system is a continuous analyzersystem that utilizes a plurality of sensors positioned to monitor theinternal conditions of each cylinder. These sensors monitor thetemperatures and pressures of the gas inside each cylinder and thevibrations at each cylinder. Such a system is often effective indetecting compressor valve damage. However, this type of system also hasdisadvantages. Significantly, this type of continuous analyzer systemcan be extremely costly because it typically requires special pressuresensors installed to measure internal cylinder pressures and adapted forsevere pulsation and a very fast response time. In addition, this systemhas high operating costs because of the severe pulsation within acompressor cylinder, which causes the load sensing diaphragm of thespecial pressure sensor to experience metal fatigue causing intermittentfailures, which require high cost replacement sensors. Further,theoretical discharge temperatures calculated with this system are ofteninaccurate, particularly for high-speed compressors, because the systemuses terminal pressure to calculate theoretical discharge temperature.That is, this system measures the internal cylinder pressure at the topand bottom of each piston stroke when the piston is stopped and at thepoint of reversing directions. As a result, the terminal pressure isusually equal to suction and discharge external flange pressure and isnot adjusted to account for true internal cylinder minimum and maximumpressures.

Accordingly, there remains a need in the art for a more practical, costeffective, and improved compressor protection method and system that iscapable of continuously establishing variable compressor dischargetemperature set points based on actual in-service conditions anddetecting damaged compressor valves for a given cylinder at each stageof compression.

BRIEF SUMMARY OF THE INVENTION

An object of this invention is to provide a more practical and costeffective compressor protection method and system capable ofcontinuously establishing variable compressor discharge temperature setpoints based on actual in-service conditions. A further object of thisinvention is to provide a compressor protection method and systemcapable of detecting damaged compressor valves for a given cylinder ateach stage of compression. Still a further object of this invention isto accurately calculate theoretical discharge temperature for acompressor. Additional objects and advantages of this invention shallbecome apparent in the ensuing descriptions of the invention.

Accordingly, a more practical, cost effective and improved compressorprotection method and system that is capable of continuouslyestablishing compressor discharge temperature set points based on actualin-service conditions and detecting damaged compressor valves for agiven cylinder at each stage of compression. The method and systemutilize sensors configured to monitor process property parameters at theinlet section and outlet section of a compressor stage. The monitoredprocess property parameters include temperature and pressure. Thesensors generate monitored signals corresponding to the process propertyparameters. The method and system also utilizes a controller configuredto receive and process these monitored signals. The controller executesa control logic that uses the monitored signals to either estimate orcalculate compressor valve pressure losses for determining internalcylinder pressures, which are used to calculate compressor dischargetemperature set points. The control logic compares the monitoredtemperature to the temperature set points and may generate a warning ornormal operation signals based on results of the comparison.

The foregoing brief summary of the invention presents a simplifiedsummary of the claimed subject matter in order to provide a basicunderstanding of some aspects of the claimed subject matter. Thissummary is not an extensive overview of the claimed subject matter. Itis intended to neither identify key or critical elements of the claimedsubject matter nor delineate the scope of the claimed subject matter.Its sole purpose is to present some concepts of the claimed subjectmatter in a simplified form as a prelude to the more detaileddescription that is presented below.

Additionally, the foregoing has outlined rather broadly the features andtechnical advantages of the present invention in order that the detaileddescription of the invention that follows may be understood. Additionalfeatures and advantages of the invention will be described hereinafter,which form the subject of the claims of the invention. It should beappreciated by those skilled in the art that the conception and specificembodiments disclosed may be readily utilized as a basis for modifyingor designing other structures for carrying out the same purposes of thepresent invention. It should also be realized by those skilled in theart that such equivalent constructions do not depart from the spirit andscope of the invention as set forth in the appended claims. The novelfeatures, which are believed to be characteristic of the invention, bothas to its organization and method of operation, together with furtherobjects and advantages will be better understood from the followingdescription when considered in connection with the accompanying figures.It is to be expressly understood, however, that each of the figures isprovided for the purpose of illustration and description only and is notintended as a definition of the limits of the present invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

The accompanying drawings illustrate preferred embodiments of thisinvention. However, it is to be understood that these embodiments arenot intended to be exhaustive, nor limiting of the invention. Theseembodiments are but examples of some of the forms in which the inventionmay be practiced.

FIG. 1 illustrates a process and instrument diagram for an embodiment ofa compressor protection system in accordance with this invention usedwith a multi-stage reciprocating compressor.

FIG. 2 illustrates a block diagram of a compressor protection methodhaving a first warning signal and a second warning signal in accordancewith this invention.

FIG. 3 illustrates a block diagram of a compressor protection methodhaving a first warning signal in accordance with this invention.

FIGS. 4, 5, and 6 illustrate examples of simplified displays that may beshown on a display device in accordance with this invention.

DETAILED DESCRIPTION OF THE INVENTION

The claimed subject matter is now described with reference to thedrawings, wherein like reference numerals are used to refer to likeelements throughout. FIG. 1 illustrates an embodiment of a compressorprotection system in accordance with this invention used with amulti-stage reciprocating compressor. Although the subsequent discussionis in reference to a multi-stage reciprocating compressor, thecompressor protection system may also be used with any compressor thatincreases the pressure of a gas by alternatively filling and discharginga cylinder, including a single-stage reciprocating compressor.

As shown generally at 100, a multi-stage reciprocating compressorcomprises a first compression stage (110) and second compression stage(120) with each stage having at least one cylinder. The cylinders areconfigured to increase the pressure of a gas by the movement of apiston, plunger or diaphragm in the cylinder. Each compression stage(110, 120) has an inlet or suction section (111, 121) configured toreceive a gas and an outlet or discharge (112, 122) section configuredto discharge the gas. The inlet section comprises inlet piping and aninlet compressor valve, and the outlet section comprises outlet pipingand an outlet compressor valve.

The reciprocating compressor may also comprise a knock-out vessel (113,123, 133) configured to separate the liquid and gas phases of a fluid.The knock-out vessels (113, 123, 133) are preferably located at leastupstream of the compression stages (110, 120) and/or downstream of anyheat-exchangers to ensure most entrained liquids are substantiallyseparated from the fluid prior to it entering the compression stage(110, 120). Each knock-out vessel (113, 123, 133) typically has an inletto receive a gas, a liquid outlet, and a vapor outlet. The knock-outvessel (113, 123, 133) may also include a mist eliminator, such as amesh pad or baffles, configured to minimize the entrainment of anyliquid droplets in the gas. The knock-out vessel may be sized andoriented (e.g. horizontal, vertical) in any manner that substantiallyremoves liquid from the gas. Suitable design guidelines for knock-outvessels are well-known in the art, e.g. A. Kayode Coker, Ernest E.Ludwig (2007). Ludwig's Applied Process Design for Chemical andPetrochemical Plants (Volume 1, 4^(th) edition). Burlington: GulfProfessional Publishing.

The reciprocating compressor may further comprise a heat exchanger (114,124), such as an intercooler, configured to receive a gas and remove theheat of compression from the gas. The heat exchanger (114, 124) ispreferably located following the outlet of the compression stage (110,120). As the fluid passes through the heat exchanger (114, 124), it iscooled and the gas phase may partially or fully condense to a liquid. Asdiscussed above, in order to prevent possible equipment damage, it ispreferable to route the gas from the heat exchanger to a knock-outvessel to substantially remove any liquids before sending the gas to thecompression stage. Suitable design guidelines for heat exchangers arewell-known in the art, e.g. A. Kayode Coker, Ernest E. Ludwig (2007).Ludwig's Applied Process Design for Chemical and Petrochemical Plants(Volume 1, 4^(th) edition). Burlington: Gulf Professional Publishing.

The compressor protection system comprises a plurality of sensors (115,116, 117, 118, 125, 126, 127, 128). The sensors are configured tomonitor selected process property parameters at the inlet section (111,121) and outlet section (112, 122) of a compression stage and generate aplurality of monitored signals corresponding to the selected processproperty parameters. The selected process property parameters correspondto actual in-service operating conditions. The sensors may be new orexisting, which include sensors that are part of an existing control ormonitoring system.

The selected process property parameters include those required forcalculation methods, which are well-known in the art, that sufficientlyapproximate pressure losses and compressor discharge temperature. Forexample, pressure losses associated with gas flowing through compressorvalves (and other valves), pipe and fittings may be calculated usingderivations of the Bernoulli theorem as detailed in several publicationsknown in the art such as Crane Co. (2009, September). Flow of FluidsThrough Valves, Fittings and Pipe (Technical Paper No. 410). Stamford,Conn. Compressor valve pressure losses may also be sufficientlyapproximated using data obtained by observation during periodiccompressor performance testing by instruments with internal pressuresensors (e.g. internal pressure sensors available from Windrock and BetaCorporation, compressor manufacturer performance calculation method(s)(e.g. Ariel Corporation. (2001). Application Manual Ariel CalculationMethod. Mount Vernon, Ohio.), or compressor manufacturer performanceprogram(s) (e.g. Ariel Corporation Performance Program all versions).

Examples of selected process property parameters that may be monitoredto calculate pressure losses include, but are not limited to, pressure,temperature, piston diameter, valve area(s), piston speed, gas flowrate, gas composition, k value (the ratio of specific heats (Cp/Cv)),gas specific gravity, viscosity, molecular weight, and so forth. As oneof ordinary skill in the art appreciates, the gas specific gravity and kvalue may be determined by use of data tables from reference manuals(e.g. Perry's Chemical Engineer's Handbook which is hereby incorporatedby reference in its entirety (Don W. Perry, Robert H. Perry (2008).Perry's Chemical Engineer's Handbook (8^(th) edition), McGraw-Hill.), orby use of computer programs or simulators known to those of ordinaryskill in the art (e.g. use of the Ariel Performance Program by input ofa representative or actual gas analysis will yield both the k value andthe gas specific gravity).

Process property parameters that may be monitored to calculatecompressor discharge temperature include those required for calculationmethods using the adiabatic gas compression temperature calculationmethod, which is well-known in the art. The adiabatic gas compressiongas compression temperature may be calculated by the following equation:

$T_{dc} = {T_{s} \times ( \frac{P_{d}}{P_{s}} )^{\frac{k - 1}{k}}}$

where T_(dc) is calculated compressor discharge temperature (degreesRankine), T_(s) is the monitored compressor suction temperature (degreesRankine), P_(d) is calculated or estimated outlet internal compressorcylinder pressure (psia), P_(s) is calculated or estimated inletinternal compressor cylinder pressure (psia), and k is the ratio ofspecific heats or k value of the compressed gas (dimensionless). Othercalculation methods similar to the adiabatic gas compression calculationmethods may also be used. For examples, the polytropic gas compressionformula, which is well-known in the art, may also be used to calculatecompressor discharge temperature.

Examples of selected parameters that may be monitored to calculatecompressor discharge temperature include, but are not limited to, gaspressure, gas temperature, compressor speed, gas composition, gasspecific gravity, and so forth. Some of these process propertyparameters may also be derived from other process property parametersusing other calculation methods, computer simulation packages, or gasproperty tables.

As shown in FIG. 1, the compressor protection system comprises aplurality of sensors configured to monitor gas temperature (116, 118,126, 128) and gas pressure (115, 117, 125, 127) located at the inlet(111, 121) and outlet (112, 122) of each compression stage. Thetemperature and pressure sensors generate signals corresponding to themonitored temperatures and pressures. The temperature (116, 118, 126,128) and pressure sensors (115, 117, 125, 127) may be located at anylocation that provides a representative and sufficiently accuratemeasurement of the temperature and pressure at or near the inlet (oroutlet) of each compressor cylinder within a stage. Locating the sensorsin these locations eliminates the requirement for special sensors tomeasure internal cylinder pressures. The temperature and pressuresensors should also be compatible with the gas and design conditions ofthe reciprocating compressor system.

In an embodiment, the compressor protection system has at least oneinlet temperature sensor (116, 126) and at least one inlet pressuresensor (115, 125) located at or near the inlet of each compressionstage. Additional inlet temperature and pressure sensors may be providedin order to provide redundant measurements to verify measurements and soforth if desired. The sensors (115, 116, 125, 126) are preferablylocated as close as practical to the inlet of the compressor cylinder;however, as discussed above, these sensors (115, 116, 125, 126) may belocated at any location that provides a representative and sufficientlyaccurate measurement of the temperature and pressure at or near theinlet of each compressor cylinder within a stage. Examples of suitablesensor locations include, but are not limited to, a suction vessel suchas a pulsation vessel, knock-out vessel, and so forth.

The compressor protection system also has at least one outlet pressuresensor (115, 125) located at or near the outlet of the compressionstage. Additional outlet pressure sensors may be provided in order toprovide redundant measurements to verify measurements and so forth ifdesired. The outlet pressure sensor is preferably located as close aspractical to the outlet of the compressor cylinder however, as discussedabove, these sensors (115, 116, 125, 126) may be located at any locationthat provides a representative and sufficiently accurate measurement ofthe temperature and pressure at or near the outlet of each compressorcylinder within a stage. Examples of suitable sensor locations include,but are not limited to, a suction vessel such as a pulsation vessel,knock-out vessel, and so forth.

The compressor protection system also includes at least one outlettemperature sensor (118, 128) for each cylinder within the compressorstage. Additional outlet temperature sensors (118, 128) may be providedin order to provide redundant measurements to verify measurements and soforth if desired. Sensors are provided at or near the outlet of eachcylinder in order to discriminate which cylinder may be experiencingvalve failure. The outlet temperature sensor (118, 128) should belocated as close as practical to the outlet of each compressor cylinderwithin a compressor stage, e.g. between the compressor cylinder and thecompressor discharge nozzle, to ensure a sufficiently accuraterepresentative measurement of the discharge temperature of the gas. Thecompressor discharge nozzle is typically directly attached to thecompressor cylinders. The outlet temperature sensor (118, 128) may alsobe located at other locations provided that care is taken to obtain arepresentative discharge temperature of the gas from the compressorcylinder. In addition, outlet temperatures sensor may be added at thelocation of each compressor outlet valve, typically through the valveretaining mechanical devices, to discriminate individual gastemperatures at each valve, and thereby detect individual outlet valvefailures.

The compressor protection system further comprises a controller (140).The controller (140) is capable of receiving the monitored selectedprocess property parameters, and performing the required calculations ona continuously updating basis. Such a controller would typically be aprogrammed microprocessor configured to receive and process themonitored signals transmitted from the plurality of sensors viaelectrical connections (e.g. electrical wires, data transmission cables,etc.) or by wireless signals transmitted over a wireless network. Thesignals may be direct analog signals or digital communication signals.The controller (140) is also configured to execute control logic forperforming various analyses including calculating operating set points,comparing the set points with the monitored signals, generating alarmsignals, and so forth. The controller (140) may be integrated into a newor existing control system, including additional programming of aprogrammable logic controller (PLC) system, or human machine interface(HMI) with sufficient excess processing capability, or other means.Examples of suitable controllers include, but are not limited to,Altronic DE series control systems, Murphy Millennium and Centurionsystems, Allen Bradley PLC systems, Red Lion, and so forth.

The compressor protection system may also include a computing device ordisplay device (150) configured to receive signals such as warningsignals, monitored selected process property parameter signals, setpoints, alarms, and so forth. The display device (150) may also beconfigured to display the warning signals as well as other informationsuch as monitored compressor speed and selected process propertyparameters from the sensors, calculated variables, and so forth. FIGS.4, 5, and 6 illustrate examples of simplified displays (400, 500, 600)that may be shown on a display device in accordance with this invention.

Turning now to FIG. 2, in operation, the compressor protection systemutilizes a controller configured to execute a control logic comprising aprocess property parameter collection component, an internal cylinderpressure calculation component, a temperature set point calculation andcomparison component, and a signal component.

The process property parameter collection component comprises using thesensors to collect selected process property parameters (201) andgenerate a plurality of monitored signals corresponding to the collectedproperty parameters. The sensors are configured to continuously collectdata and transmit signals to the controller. The time period over whichthe sensors collect selected property parameter data and transmitcorresponding signals typically depends on the compressor system. Thesensors may collect data and transmit signals over a time period of lessthan one second. However, the compression protection system and methodmay be just as effective over a longer period of time, e.g. fifteenminutes.

In a preferred embodiment, the sensors collect gas temperature andpressure data at the inlet and outlet of each compression stage. Sensorsmay also be provided to collect compressor speed data and/or atmosphericpressure data. The sensors then generate signals corresponding to thecollected data and transmit the signals to the controller. In additionto the temperature and pressure data, the ratio of specific heats of thegas entering each compression stage should also be determined. The ratioof specific heats may be a fixed input into the controller as a constantvalue based on known from an actual or representative gas analysis ofthe gas entering the compressor used in conjunction with knowncalculation methods, computer simulation packages, or gas propertytables. Alternatively, the ratio of specific heats may also becontinuously updated using data transmitted from a sensor configured tomeasure required properties to determine the ratio of specific heats.The sensor may include an output signal, either in digital or analogform that may be used as a continuous input value for calculations inthe compressor protection system. An example of a suitable sensorconfigured to determine the ratio of specific heats include, but are notlimited to, a continuous gas analyzer available by and from Dynalco,Windrock, Beta, Hoerbiger, and so forth.

The internal cylinder pressure calculation component comprisesdetermining the pressure loss associated with the flow of the gasthrough the compressor cylinder inlet valve(s) and outlet valve(s)(202). The internal cylinder pressure calculation component determinesthe pressure loss by either estimating or calculating the pressure lossusing monitored selected process property parameter data and deriving atheoretical internal compressor cylinder inlet pressure and outletpressure. The resultant internal compressor inlet pressure and outletpressure are then used to calculate a predicted compressor dischargetemperature. The resultant internal compressor inlet pressure and outletpressure may also be adjusted in proportion to the compressor speed.

The internal compressor cylinder pressures may be determined using thefollowing equations:

P _(s) =P _(i) −P _(icv)

P _(d) =P _(o) +P _(ocv),

where P_(s) is inlet or suction internal compressor cylinder pressure(psia), P_(i) is pressure monitored by the inlet pressure sensor (psia),is inlet compressor valve pressure loss (psia), P_(d) is outlet ordischarge internal compressor cylinder pressure (psia), P_(o) ispressure monitored by the outlet pressure sensor (psia), and P_(ocv) isoutlet compressor valve pressure loss (psia).

Compressor valve pressure loss may be determined by either using fixedcondition estimates with adjustments for variable speed where necessaryor continuously calculated. Fixed condition estimates of pressure lossmay be determined using multiple sources. Example sources include, butare not limited to, data obtained by observation during periodiccompressor performance testing by instruments with internal pressuresensors (e.g. internal pressure sensors available from Windrock, or BetaCorporation, or Bentley-Nevada part #165855, compressor manufacturersperformance calculation method or performance program (e.g. ArielCorporation Performance Program all versions, Ariel CorporationCalculation Method), and derivations of the Bernoulli theorem asdetailed in several publications known in the art such as Crane Co.(2009, September). Flow of Fluids Through Valves, Fittings and Pipe(Technical Paper No. 410). Stamford, Conn.

The fixed condition estimates of pressure loss should be at the ratedspeed of the compressor. In cases where the compressor system operatesat variable speeds, the fixed condition pressure loss should be updatedcontinuously by methods described below. The fixed condition pressureloss may be adjusted by linear reduction of the fixed condition pressureloss in direct proportion of the actual compressor speed to the ratedcompressor speed. Alternatively, the fixed condition pressure loss mayalso be adjusted by exponential reduction of the pressure loss estimatein proportion to the actual compressor speed relative to the ratedcompressor speed, e.g. pressure loss is typically directly proportionalto the square of the compressor speed.

Determining pressure losses based on fixed condition estimates ispreferably used in cases where the compressor inlet pressure and outletpressure conditions are substantially fixed. Substantially fixedconditions are generally required for the estimates of valve pressurelosses to be sufficiently accurate for the intended purpose. It ispreferred that compressor stage inlet and outlet pressures are withinabout +/−20% of those associated with the valve pressure loss estimatesfor the fixed conditions. Further, the fixed condition estimates ofvalve pressure losses are expected to be sufficiently accurate where thecompressed gas specific gravity varies from the fixed conditionreference specific gravity by about +/−8%. For compressed gases with avariable specific gravity, continuously calculated methods should beused. Examples of gases with a variable specific gravity include, butare not limited to, field gas gathering operations, mixed gas streams ingas processing operations, gas blending operations, or other operationswhich variably mix gasses of different specific gravities.

As discussed above, valve pressure losses may also be continuouslycalculated using sensors configured to monitor selected process propertyparameters necessary to calculate pressure loss. Continuous calculationsof valve pressure losses may be determined using data obtained either byobservation during periodic compressor performance testing withinstruments with internal pressure sensors, or compressor manufacturersperformance calculation method or performance program (e.g. ArielCorporation Performance Program all versions, Ariel CorporationCalculation Method). The data should be obtained over the anticipatedrange of operation of the compressor system. The data may also be madeavailable for continuous calculations using a lookup table. Continuouscalculations of valve pressure losses may also be determined usingderivations of the Bernoulli theorem as detailed in several publicationsknown in the art such as Crane Co. (2009, September). Flow of FluidsThrough Valves, Fittings and Pipe (Technical Paper No. 410). Stamford,Conn.

In addition to adjusting the monitored pressures for compressor valvepressure loss, the internal cylinder pressure calculation component mayalso calculate a pressure loss associated with the gas flow between theinlet pressure sensor and inlet compressor valve as well as the pressureloss between the outlet pressure sensor and outlet compressor valve.These pressure losses may account for pressure loss associated with gasflow through any pipe, fittings, equipment, or other valves that may bebetween the pressure sensor and the compressor valve. When accountingfor pressure loss associated with both compressor valves, pipe fittings,and other valves, the internal compressor cylinder pressures may bedetermined using the following equations:

P _(s) =P _(i) −P _(icv) −P _(iline)

P _(d) =P _(o) +P _(ocv) +P _(oline)

where P_(iline) is the pressure loss of gas flowing through pipe,fittings, and other valves between the inlet pressure sensor and inletcompressor valve pressure loss (psia), and P_(oline) is the pressureloss of gas flowing through pipe, fittings, and other valves between theoutlet pressure sensor and outlet compressor valve pressure loss (psia).Pressure loss associated with gas flow through pipes, fittings, andother valves may be determined using estimates from compressormanufacturers or calculated using derivations of the Bernoulli theoremas discussed above.

The temperature set point calculation and comparison component comprisesusing the calculated internal compressor cylinder pressures andcollected process property parameter data to calculate the calculatedcompressor discharge temperature (T_(dc)) using the equation discussedabove. The temperature set points for equipment shutdown protectionshould be calculated based on the calculated discharge temperature andadjusted by a fixed value and/or a percentage value, and continuouslycompared to the actual compressor discharge temperature. In addition,operator notification by an alarm is desirable. Such alarm dischargetemperature set point values may be calculated based on the calculateddischarge temperatures and adjusted by a fixed value and/or a percentagevalue and continuously compared to the actual compressor dischargetemperature. The percentage and fixed values to accomplish the alarm andshutdown protection are more fully described below.

The temperature set point calculation and comparison componentcalculates a first and second temperature set point (203) for thecompressor outlet (discharge) temperature for a given compression stage.The first temperature set point may be calculated using the followingequation:

T _(SP1) =T _(dc) ×C ₁

where T_(SP1) is the first temperature set point (degrees Rankine),T_(dc) is calculated compressor discharge temperature (degrees Rankine),and C₁ is a first constant (dimensionless). The value of the firstconstant is selected based on the amount that the monitored compressordischarge temperature (T_(d)) may exceed the calculated compressordischarge temperature (T_(dc)) before generating a first warning signal.For example, if it is desired that the monitored compressor dischargetemperature only exceed the calculated compressor discharge temperatureby 12% before generating a first warning signal, then the first constanthas a value of 1.12. As one of ordinary skill in the art appreciates,the value used for C₁ may be selected by the end user as desired and/oron an application basis.

The first temperature set point may also be calculated using thefollowing equation:

T _(SP1) =T _(dc) +C ₂

where T_(SP1) is the first temperature set point (degrees Rankine),T_(dc) is calculated compressor discharge temperature (degrees Rankine),and C₂ is a second constant (dimensionless). As with the first constant,the value of the second constant is selected based on the amount thatthe monitored compressor discharge temperature (T_(d)) may exceed thecalculated compressor discharge temperature (T_(dc)) before generating afirst warning signal. However, instead of a fixed percentage, the secondconstant is a fixed value. For example, if it is desired that themonitored compressor discharge temperature only exceed the calculatedcompressor discharge temperature by 15 degrees before generating a firstwarning signal, then the first constant has a value of 15. As one ofordinary skill in the art appreciates, the value used for C₂ may beselected by the end user as desired and/or on an application basis.

The second temperature set point may be calculated using the followingequation:

T _(SP2) =T _(dc) ×C ₃

where T_(SP2) is the second temperature set point (degrees Rankine),T_(d), is calculated compressor discharge temperature (degrees Rankine),and C₃ is a third constant (dimensionless). The value of the thirdconstant is selected based on the amount that the monitored compressordischarge temperature (T_(d)) may exceed the calculated compressordischarge temperature (T_(dc)) before generating a second warningsignal. For example, if it is desired that the monitored compressordischarge temperature only exceed the calculated compressor dischargetemperature by 22% before generating the second warning signal, then thethird constant has a value of 1.22. As one of ordinary skill in the artappreciates, the value used for C₃ may be selected by the end user asdesired and/or on an application basis. The second temperature set pointmay also be calculated using the following equation:

T _(SP2) =T _(dc) +C ₄

where T_(SP2) is the second temperature set point (degrees Rankine),T_(dc) is calculated compressor discharge temperature (degrees Rankine),and C₄ is a fourth constant (dimensionless). As with the third constant,the value of the fourth constant is selected based on the amount thatthe monitored compressor discharge temperature (T_(d)) may exceed thecalculated compressor discharge temperature (T_(dc)) before generating asecond warning signal. However, instead of a fixed percentage, thefourth constant is a fixed value. For example, if it is desired that themonitored compressor discharge temperature only exceed the calculatedcompressor discharge temperature by 15 degrees before generating asecond warning signal, then the fourth constant has a value of 15. Asone of ordinary skill in the art appreciates, the value used for C₄ maybe selected by the end user as desired and/or on an application basis.The constants (C1, C2, C3, and/or C4) may be preprogrammed into thecontroller.

The temperature set point calculation and comparison component furthercomprises comparing the first temperature set point to the monitoredcompressor discharge temperature (204) to determine if the two valuesare consistent or inconsistent with one another. The signal componentuses results of the temperature set point calculation and comparisoncomponent to generate signals such as a normal operation signal, awarning signal, and so forth. If the monitored compressor dischargetemperature is less than the first temperature set point (205), then thecontroller generates a normal operation signal (206) and returns to theinitial step of collecting selected process property parameters (201).However, if the monitored compressor discharge temperature is greaterthan or equal to the first temperature set point (205), then thecontroller generates a first warning signal (207). The controller mayexecute a control logic that sends the first warning signal or normaloperation signal to a computer device or display device (208) so that itmay be displayed to an operator. The aforementioned signal generationand display steps may occur simultaneously.

If the controller generates the first warning signal, the controller hascontrol logic that then compares the second temperature set point to themonitored compressor discharge temperature (209). If the monitoredcompressor discharge temperature is less than the second temperature setpoint (210), then the controller returns to the initial step ofcollecting selected process property parameters (201). However, if themonitored compressor discharge temperature is greater than or equal tothe second temperature set point (210), then the controller generates asecond warning signal (211). The controller may execute a control logicthat sends the second warning signal to a computer device or displaydevice (212) so that it may be displayed to an operator. The controllermay also execute a control logic that initiates compressor shutdown(213) upon generation of the second warning signal to prevent damage tocompressor valves for a given cylinder. The compressor may be shut downby the controller or an existing control system switching off the poweror fuel source to the compressor. The aforementioned signal generation,display steps and shutdown steps may occur simultaneously.

As shown in FIG. 3, in an alternate embodiment the compressor protectionsystem may initiate a compressor shutdown upon generation of a firstwarning signal. The compressor protection system utilizes a controllerhaving control logic configured to execute a process property parametercollection component. The process property parameter collectioncomponent uses the one or more sensors to collect selected processproperty parameters (301) and generate a plurality of monitored signalscorresponding to the selected process property parameters. The controllogic further comprises and internal cylinder pressure calculationcomponent configured determine the pressure loss associated with the gasflowing between the inlet and outlet pressure sensors (302). The controllogic also comprises a temperature set point calculation and comparisoncomponent that uses the results from the internal cylinder pressurecomponent to calculate the calculated compressor discharge temperature(T_(dc)) and a first temperature set point (303). The control logic foraforementioned steps (301, 302, 303) operates in the same manner assteps discussed above (201, 202, 203) for the embodiment of FIG. 2except that the control logic does not calculate a second temperatureset point.

The temperature set point calculation and comparison component thencompares the first temperature set point to the monitored compressordischarge temperature (304) to determine if the two values areconsistent or inconsistent with one another. A signal component usesthese comparison results to generate signals. If the monitoredcompressor discharge temperature is less than the first temperature setpoint (305), then the controller generates a normal operation signal(306) and returns to the initial step of collecting selected processproperty parameters (301). However, if the monitored compressordischarge temperature is greater than or equal to the first temperatureset point (305), then the controller generates a first warning signal(307). The controller may execute a control logic that shows the firstwarning signal on a computer device or display device (308) andinitiates compressor shutdown (309) to prevent damage to compressorvalves for a given cylinder. The compressor may be shut down by thecontroller or an existing control system switching off the power or fuelsource to the compressor. The aforementioned signal generation, displaysteps and shutdown steps may occur simultaneously.

The present invention described in detail above provides significantadvantages over the prior art. In particular, the present invention is amore versatile, cost effective, and improved compressor protectionmethod and system that is capable of continuously establishing variablecompressor discharge temperature set points based on actual in-serviceconditions and detecting damaged compressor valves for a given cylinderat each stage of compression. Further, instead of requiring a pluralityof sensors installed in each cylinder at its inlet and outlet as well asvibration sensors at each cylinder, the present invention may operatewith temperature and pressure sensors installed only at the inlet andoutlet of each compression stage.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims. Moreover, thescope of the present application is not intended to be limited to theparticular embodiments of the process, machine, manufacture, compositionof matter, means, methods and steps described in the specification. Asone of ordinary skill in the art will appreciate from the disclosure ofthe present invention, processes, machines, manufacture, compositions ofmatter, means, methods, or steps, presently existing or later to bedeveloped that perform substantially the same function or achievesubstantially the same result as the corresponding embodiments describedherein may be utilized according to the present invention. Accordingly,the appended claims are intended to include within their scope suchprocesses, machines, manufacture, compositions of matter, means,methods, or steps.

What is claimed is:
 1. A method for protecting a compressor with atleast one compression stage having at least one cylinder, an inletsection configured to receive a gas wherein the inlet section comprisesinlet piping and an inlet compressor valve, an outlet section configuredto discharge the gas wherein the outlet section comprises outlet pipingand an outlet compressor valve, sensors configured to monitor selectedprocess property parameters at the inlet section and outlet section andgenerate monitored signals corresponding to the process propertyparameters, and a controller configured to receive the monitoredsignals, execute a control logic and generate signals, the control logiccomprising: a. a process property parameter collection componentcomprising: i. collecting data for the monitored selected processproperty parameters at the inlet section and outlet section using thesensors, wherein the monitored process property parameters comprise gasinlet temperature, gas inlet pressure, gas outlet temperature, gasoutlet pressure, and compressor speed; b. an internal cylinder pressurecalculation component comprising: i. determining an inlet internalcylinder pressure; ii. determining an outlet internal cylinder pressure;c. a temperature set point calculation and comparison componentcomprising: i. calculating a first outlet temperature set point for eachcylinder; ii. comparing the first outlet temperature set point with themonitored gas outlet temperature for each cylinder; d. a signalcomponent comprising: i. generating a normal operation signal if themonitored outlet temperature is consistent with the first outlettemperature set point. ii. generating a first warning signal if themonitored outlet temperature is inconsistent with the first outlettemperature set point.
 2. A method for protecting a compressor accordingto claim 1 wherein: a. the inlet internal cylinder pressure isdetermined by calculating a first pressure loss for the inlet compressorvalve; b. the outlet internal cylinder pressure is determined bycalculating a second pressure loss for the outlet compressor valve.
 3. Amethod for protecting a compressor according to claim 1 wherein: a. theinlet internal cylinder pressure is determined by estimating a firstpressure loss for the inlet compressor valve; b. the outlet internalcylinder pressure is determined by estimating a second pressure loss forthe outlet compressor valve.
 4. A method for protecting a compressoraccording to claim 2 wherein the first pressure loss and second pressureloss are adjusted in proportion to the compressor speed.
 5. A method forprotecting a compressor according to claim 4 wherein the signalcomponent further comprises: a. initiating compressor shutdown if themonitored outlet temperature is inconsistent with the first outlettemperature operating range.
 6. A method for protecting a compressoraccording to claim 5 wherein the temperature set point calculation andcomparison component further comprises: a. calculating a second outlettemperature set point for each cylinder; b. comparing the second outlettemperature set point with the monitored outlet temperature for eachcylinder.
 7. A method for protecting a compressor according to claim 6wherein the signal component further comprises: a. generating a secondwarning signal if the monitored outlet temperature is inconsistent withthe second outlet temperature set point; b. initiating compressorshutdown if the outlet temperature is inconsistent with the secondoutlet temperature operating range.
 8. A method for protecting acompressor according to claim 7 wherein the process property parametercollection component further comprises: a. collecting data using asensor configured to measure required properties to determine the ratioof specific heats.
 9. A method for protecting a compressor according toclaim 8 wherein the pressure losses are calculated using fixed operatingconditions.
 10. A method for protecting a compressor according to claim8 wherein the pressure losses are continuously calculated using actualoperating conditions.
 11. A protection system for a compressor with atleast one compression stage having at least one cylinder, an inletsection configured to receive a gas and an outlet section configured todischarge the gas, wherein the inlet section comprises inlet piping andan inlet compressor valve and the outlet section comprises outlet pipingand an outlet compressor valve, wherein the protection system comprises:a. a plurality of sensors configured to monitor selected processproperty parameters at the inlet section and outlet section and generatea plurality of monitored signal corresponding to the selected processproperty parameters; b. a controller configured to execute a controllogic, wherein the control logic comprises: i. a process propertyparameter collection component; ii. an internal cylinder pressurecalculation component; iii. a temperature set point calculation andcomparison component; iv. a signal component.
 12. A protection systemfor a compressor according to claim 11 wherein a. the process propertyparameter collection component comprises: i. collecting data for themonitored process property parameters at the inlet section and outletsection using the sensors, wherein the monitored process propertyparameters comprise gas inlet temperature, gas inlet pressure, gasoutlet temperature for each cylinder, gas outlet pressure, andcompressor speed; b. the internal cylinder pressure calculationcomponent comprises: i. determining an inlet internal cylinder pressure;ii. determining an outlet internal cylinder pressure.
 13. A protectionsystem for a compressor according to claim 12 wherein: a. the inletinternal cylinder pressure is determined by calculating a first pressureloss for the inlet compressor valve; b. the outlet internal cylinderpressure is determined by calculating a second pressure loss for theoutlet compressor valve.
 14. A protection system for a compressoraccording to claim 12 wherein: a. the inlet internal cylinder pressureis determined by estimating a first pressure loss for the inletcompressor valve; b. the outlet internal cylinder pressure is determinedby estimating a second pressure loss for the outlet compressor valve.15. A protection system for a compressor according to claim 13 whereinthe first pressure loss and second pressure loss are adjusted inproportion to the compressor speed.
 16. A protection system for acompressor according to claim 15 wherein the temperature set pointcalculation and comparison component comprises: a. calculating a firstoutlet temperature set point; b. comparing the first outlet temperatureset point with the monitored outlet temperature.
 17. A protection systemfor a compressor according to claim 16 wherein the signal componentfurther comprises: a. generating a normal operation signal if themonitored outlet temperature is consistent with the first outlettemperature set point. b. generating a first warning signal if themonitored outlet temperature is inconsistent with the first outlettemperature set point.
 18. A protection system for a compressoraccording to claim 17 wherein the signal component further comprises: a.initiating compressor shutdown if the monitored outlet temperature isinconsistent with the first outlet temperature operating range.
 19. Aprotection system for a compressor according to claim 18 wherein thetemperature set point calculation and comparison component furthercomprises: a. calculating a second outlet temperature set point for eachcylinder; b. comparing the second outlet temperature set point with themonitored outlet temperature for each cylinder.
 20. A protection systemfor a compressor according to claim 19 wherein the signal componentfurther comprises: a. generating a second warning signal if themonitored outlet temperature is inconsistent with the second outlettemperature set point; b. initiating compressor shutdown if the outlettemperature is inconsistent with the second outlet temperature operatingrange.
 21. A protection system for a compressor according to claim 20wherein the process property parameter collection component furthercomprises: a. collecting data using a sensor to configured to measurerequired properties to determine the ratio of specific heats.
 22. Aprotection system for a compressor according to claim 21 wherein thepressure losses are calculated using fixed operating conditions.
 23. Aprotection system for a compressor according to claim 21 wherein thepressure losses are continuously calculated using actual operatingconditions.